Magnetic tunnel junction device and method for fabricating the same

ABSTRACT

A magnetic tunnel junction device includes a first electrode having a curved top surface, a magnetic tunnel junction layer formed along the top surface of the first electrode, and a second electrode formed on the magnetic tunnel junction layer.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2011-0069464, filed on Jul. 13, 2011, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor memory device and amanufacturing method thereof, and more particularly to a magnetic tunneljunction device using a magnetic tunnel junction layer and a fabricatingmethod thereof.

As semiconductor memory technologies have been developed for highlyintegrated memory, a Magnetic Random Access Memory (MRAM) would becomewidely used among all types of memories because the MRAM has advantageson integration, operating speed, non-volatility. The MRAM includes atransistor configured to perform a switching function and a MagneticTunnel Junction (MTJ) device configured to store information. The MTJdevice includes a magnetic tunnel junction layer and electrodes formedthe top and bottom portions of the magnetic tunnel junction layer,wherein the magnetic tunnel junction layer includes two ferromagneticlayers and a tunnel barrier layer arranged therebetween. The magnetictunnel junction layer has different Magneto-resistance (MR) depending onmagnetization directions of the two ferromagnetic layers. Using thevariation in voltage or current caused by the variation of the MR, itmay be determined whether information stored in the MTJ indicates alogic level of “0” or “1”.

The MTJ device has a thin insulating layer between two magnetic layers.One of the magnetic layers, i.e., a free layer, has a free state wheremagnetization direction is easily changed when current flows. The other,i.e., a pinned layer, has magnetization direction set to a particularpolarity. If the two magnetic layers have the same magnetizationdirection, resistance becomes low so that electrons can easily passthrough them. This is a case that the stored data is recognized as alogic high level “1”. Otherwise, if the two magnetic layers have theopposite magnetization directions, resistance becomes high so thatelectrons hardly pass through them. This is a case that the stored datais recognized as a logic low level “0”.

In conventional MRAM, there may be a disadvantage in scalability becausean additional digit line may be required to write data into the MTJdevice. Further, magnetization process to a particular cell may affectto magnetization directions of nearby cells. Thus, it may be hard tomanufacture products.

Spin-transfer torque (STT) technology makes MRAM modify above-mentionedfeatures. A Spin-transfer torque Random Access Memory (SU-RAM) is socalled as a Spin-transfer torque Magnetic Random Access Memory(STT-MRAM) in an advanced form of MRAM. At very small device scales, aspin-polarized current may transfer its spin angular momentum to a smallmagnetic element in the spin-transfer torque random access memory(STT-RAM). When a high density current passes through a ferromagneticlayer, if a magnetization direction of the ferromagnetic layer isdifferent from spin-polarity of current, its magnetization direction maybe forcibly adjusted to have the same polarity with electrons.Accordingly, if high density current flows from the pinned layer to thefree layer, two layers have the same polarity. This is a case that thestored information is a logic high level “1”. Otherwise, when currentflows from the free layer to the pinned layer, spin accumulation occursat boundaries of a thin insulating layer so that two layers have theopposite polarities. This is a case that the stored information is alogic low level “0”.

As the STT technology applies to MRAM, write operation may be performedwithout the additional digit line, and interference between nearby cellsmay be alleviated. The SU-RAM has the advantages of lower powerconsumption and better scalability over conventional MRAM. The SU-RAM isnon-volatile memory device such as a flash memory device because themagnetic direction or polarity remains in the SU-RAM even if powersupply is cut off. In addition, the SU-RAM has a faster operating speedthan the conventional SRAM or DRAM.

The STT-RAM includes the MTJ device configured to store information. TheSTT-RAM reads or writes the information based on magnetizationdirections or polarities of stacked layers in the MTJ device. However,if the MTJ device has a smaller size to increase operating speed anddensity of the STT-RAM, ferromagnetic layers included in the MTJ devicehave smaller area so as to have super paramagnetic characteristic. Inthis case, the MTJ device may not be used as an information storageelement.

Further, as the conventional SU-RAM including the MD device of a stackedlayer is scaled down, it may be difficult to control magnetizationdirection of the stacked layer so that it is more likely to malfunction.Thus, it may be hard to increase a chip yield to a desired level. As aresult, there may be a limit to make the MTJ small because ferromagneticlayers may have a secured area to prevent an occurrence of malfunction.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention are directed to amagneto-resistive random access memory (MRAM) device having a highscalability or density.

In accordance with an exemplary embodiment of the present invention, amagnetic tunnel junction device includes a first electrode having acurved top surface, a magnetic tunnel junction layer formed along thetop surface of the first electrode, and a second electrode formed on themagnetic tunnel junction layer.

In accordance with another exemplary embodiment of the presentinvention, a magnetic tunnel junction device includes a first electrodehaving a spherical structure with a protruded pillar pattern, a magnetictunnel junction layer formed along a spherical surface of the firstelectrode, an insulating layer configured to insulate the magnetictunnel junction layer from the protruded pillar pattern of the firstelectrode, and a second electrode formed on the magnetic tunnel junctionlayer.

In accordance with another exemplary embodiment of the presentinvention, a magnetic tunnel junction device includes a first electrodehaving a pillar structure, a magnetic tunnel junction layer including abottom connected to the first electrode and a top curved surface, and asecond electrode formed on the magnetic tunnel junction.

In accordance with another exemplary embodiment of the presentinvention, a magnetic tunnel junction device includes a first electrodehaving a pillar structure, a magnetic tunnel junction layer having aspherical surface and covering an upper part of the first electrode, asecond electrode formed on the magnetic tunnel junction layer, and aninsulating layer configured to electronically isolate the magnetictunnel junction layer from a side area of the upper part of the firstelectrode.

In accordance with another exemplary embodiment of the presentinvention, a method for fabricating a magnetic tunnel junction deviceincludes forming a first electrode having a curved top surface, forminga magnetic tunnel junction layer along the top surface of the firstelectrode, and forming a second electrode on the magnetic tunneljunction layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a magnetic tunnel junction(MTJ) device in accordance with an exemplary embodiment of the presentinvention.

FIG. 2 is a cross-sectional view depicting a MTJ device in accordancewith another exemplary embodiment of the present invention.

FIG. 3 is a cross-sectional view describing a MTJ device in accordancewith another exemplary embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a MTJ device in accordance withanother exemplary embodiment of the present invention.

FIGS. 5A to 5C are plane views depicting a magnetic tunnel junctionlayer included in the MTJ devices shown in FIGS. 1 to 4.

FIG. 6 is a perspective view describing a process used for fabricatingthe MTJ devices shown in FIGS. 1 to 4.

FIGS. 7A to 7F depict a method for forming the MTJ devices shown inFIGS. 1 to 4.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as being limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the present inventionto those skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

FIG. 1 is a cross-sectional view showing a magnetic tunnel junction(MTJ) device in accordance with an exemplary embodiment of the presentinvention.

As shown, the MTJ device includes a first electrode 20, a magnetictunnel junction layer 100 arranged/placed on the first electrode 20, anda second electrode 70 arranged on the magnetic tunnel junction 100.Here, a top surface of the first electrode 20 is curved or bowed, i.e.,in a convex shape.

The first electrode 20 includes a first part (lower part) having apillar shape and a second part (upper part) having a curved top surface.An insulating layer 10 surrounds the first part of the first electrode20. The second part of the first electrode 20 is formed in a dome shape.The second electrode 70 has a flat top surface because the top surfaceis planarized.

Another insulating layer (not shown) may be further included toelectrically isolate the MTJ device from other nearby MTJ devices. Theinsulating layer includes one selected from the group of an oxide layer,a nitride layer, an oxynitride layer, a carbonic layer, and a stackedlayer of combining two or more of those. As the oxide layer, a siliconoxide such as SiO₂, a boron phosphorus silicate glass (BPSG), aphosphorus silicate glass (PSG), a tetra ethyle ortho silicate (TEOS),an un-doped silicate glass (USG), a spin-on-glass (SOG), a high densityplasma (HDP) oxide, or a spin-on-dielectric (SOD) may be used. Also, asthe nitride layer, a silicon nitride such as Si₃N₄ may be used. Theoxynitride layer may include a SiON. The carbonic layer may include anamorphous carbon, a carbon rich polymer, a SiOC, or a SOC.

The first electrode 20 and the second electrode 70 may include a metalor a metal compound. As the metal, a titanium (Ti), a tantalum (Ta), aplatinum (Pt), a copper (Cu), a tungsten (W), or an aluminum (Al) may beused. The metal compound may include a titanium nitride (TiN), atantalum nitride (TaN), or a tungsten silicide (WSi). According toexemplary embodiments, the first electrode 20 and the second electrode70 are formed of the same material or different materials.

The magnetic tunnel junction layer 100 includes a free layer 30 arrangedon the first electrode 20, a tunnel insulating layer 40 arranged on thefree layer 30, a pinned layer 50 arranged on the tunnel insulating layer40, and a pinning layer 60 arranged on the pinned layer 50.

Further, in another exemplary embodiment, the magnetic tunnel junctionlayer 100 may have a stacked structure of a pinning layer, a pinnedlayer, a tunnel insulating layer, and a free layer, which are formed inorder on the first electrode 20.

The pinning layer 60 serving as fixing the magnetization direction ofthe pinned layer 50 may include anti-ferromagnetic material. As theanti-ferromagnetic material, materials marked by chemical formulae ofIrMn, PtMn, MnO, MnS, MnTe, MnF₂, FeF₂, FeCl₂, FeO, CoCl₂, CoO, NiCl₂,and NiO may be used. The pining layer 60 may include not only a singleanti-ferromagnetic layer but two or more stacked anti-ferromagneticlayers.

The pinned layer 50 is set to a particular polarity, but the free layer30 has a changeable polarity. An external stimulus such as a magneticfield or a spin transfer torque (STT) adjusts magnetization direction ofthe free layer 30. The free layer 30 and the pinned layer 50 includeferromagnetic materials. As the ferromagnetic materials, materialsmarked by chemical formulae of Fe, Co, Ni, Gd, Dy, NiFe, CoFe, MnAs,MnBi, MnSb, CrO₂, MnOFe₂O₃, FeOFe₂O₃, NiOFe₂O₃, CuOFe₂O₃, MgOFe₂O₃, EuO,and Y₃Fe₅O₁₂ may be used. The pinned layer 50 and the free layer 30 mayinclude not only a single ferromagnetic layer but two or more stackedferromagnetic layers. Further, the free layer 30 and the pinned layer 50include a stacked structure of any ferromagnetic layer and a ruthenium(Ru) layer.

In another exemplary embodiment, the pinned layer 50 and the free layer30 include a synthetic anti-ferromagnetic (SAF) layer which has asequentially stacked structure of a ferromagnetic layer,anti-ferromagnetic coupling spacer layer, and another ferromagneticlayer.

The tunnel insulating layer 40 is used as a tunneling barrier betweenthe pinned layer 50 and the free layer 30. The tunnel insulating layer40 may include a magnesium oxide (MgO), an aluminum oxide (Al₂O₃), amagnesium aluminum oxide (MgAlO), a silicon nitride (Si₃N₄), a siliconoxynitride (SiON), a silicon oxide (SiO2), a hafnium oxide (HfO₂), or azirconium oxide (ZrO₂). In addition to these materials, any materialshaving insulation characteristic may be used for the tunnel insulatinglayer 40. For example, any insulating compound might be used even thoughit includes aluminum or any material having magnetic properties.

In an exemplary embodiment, the magnetic tunnel junction layer 100 mayinclude sequentially stacked layers of an anti-ferromagnetic layer, afirst ferromagnetic layer, a tunnel insulating layer, and a secondferromagnetic layer. In another embodiment, the magnetic tunnel junctionlayer 100 includes a sequentially stacked layers of ananti-ferromagnetic layer, a first ferromagnetic layer, a rutheniumlayer, a second ferromagnetic layer, a tunnel insulating layer, and athird ferromagnetic layer. In another embodiment, the magnetic tunneljunction layer 100 includes a sequentially stacked layers of a firstferromagnetic layer, a ruthenium layer, a second ferromagnetic layer, atunnel insulating layer, and a third ferromagnetic layer. In aboveembodiments, the first to third ferromagnetic layer may include at leastone of the above-mentioned ferromagnetic materials.

In the MTJ device according to exemplary embodiments of the presentinvention, even if the MTJ device has the same area per unit as theconventional MTJ device, ferromagnetic layers included in a magnetictunnel junction layer have larger interfacial area than those of theconventional MTJ. Thus, the MTJ of the present invention may increasescalability of the MRAM device by increasing an interfacial area offerromagnetic layers and preventing the MRAM device from havingsuper-paramagnetic characteristic.

In accordance with exemplary embodiments of the present invention,because a size of single MTJ device may be reduced, the MRAM deviceincluding plural MTJ devices may be scaled down. Also, when the MTJ ofthe present invention may have the same size with those of theconventional MRAM, spin switching operation reliability of the MTJdevice increases because its interfacial area is larger than those ofthe conventional MRAM. Particularly, because a curved MTJ deviceaccording to exemplary embodiments of the present invention may achievehigh density compared to the conventional MTJ having a flattened andstacked structure, a spin-transfer torque random access memory (SU-RAM)may increase storage capacity. Also, using the MTJ device according tothe present invention, stray field reducing total magnetic moment may beprevented from being generated by the magnetization in a magnet layer sothat the SU-RAM has more operation reliability than the conventionalMRAM using a magnetic field of MTJ device.

FIG. 2 is a cross-sectional view depicting a MTJ device in accordancewith another exemplary embodiment of the present invention.

As shown, the MTJ includes a first electrode 21 having a sphericalstructure with a protruded pillar pattern, a magnetic tunnel junctionlayer 200 covering a spherical surface of the first electrode 21, aninsulating layer 11 configured to insulate the magnetic tunnel junctionlayer 200 from the protruded pillar pattern of the first electrode 21,and a second electrode (not shown) arranged on the magnetic tunneljunction 200. The magnetic tunnel junction layer 200 includes a freelayer 31 arranged on the first electrode 21, a tunnel insulating layer41 arranged on the free layer 31, a pinned layer 51 arranged on thetunnel insulating layer 41, and a pinning layer 61 arranged on thepinned layer 51.

Further, in another exemplary embodiment, the magnetic tunnel junctionlayer 200 may have a stacked structure of a pinning layer, a pinnedlayer, a tunnel insulating layer, and a free layer, which are formed inorder on the first electrode 21. The pinning layer 61, the pinned layer51, and the free layer 31 may respectively include any material used inabove-mentioned embodiment. The insulating layer 11 may also include anymaterial used in above-mentioned embodiment.

According to exemplary embodiments, the second electrode may covereither a partial area of the pinning layer 61 or whole area of thepinning layer 61.

FIG. 3 is a cross-sectional view describing a MTJ device in accordancewith another embodiment of the present invention.

As shown, the MTJ device includes a first electrode 22 having a pillarstructure, a magnetic tunnel junction layer 300 including a bottomsurface connected to the first electrode 22 and a top bowed surface, anda second electrode (not shown) arranged on the magnetic tunnel junction300. The magnetic tunnel junction layer 300 includes a free layer 32arranged on the first electrode 22, a tunnel insulating layer 42arranged on the free layer 32, a pinned layer 52 arranged on the tunnelinsulating layer 42, and a pinning layer 62 arranged on the pinned layer52.

Further, in another exemplary embodiment, the magnetic tunnel junctionlayer 300 may have a stacked structure of a pinning layer, a pinnedlayer, a tunnel insulating layer, and a free layer, which are formed inorder on the first electrode 22. The pinning layer 62, the pinned layer52, and the free layer 32 may respectively include any material used inabove-mentioned embodiment.

FIG. 4 is a cross-sectional view showing a MTJ device in accordance withanother exemplary embodiment of the present invention.

As shown, the MTJ device includes a first electrode 23 having a pillarstructure, a magnetic tunnel junction layer 400 covering a set portionat an upper area of the first electrode 23, a second electrode (notshown) arranged on the magnetic tunnel junction, and an insulating layer12 configured to electronically isolate the magnetic tunnel junction 400from a side area of the first electrode 23.

The magnetic tunnel junction layer 400 includes a free layer 33 arrangedon the first electrode 23, a tunnel insulating layer 43 arranged on thefree layer 33, a pinned layer 53 arranged on the tunnel insulating layer43, and a pinning layer 63 arranged on the pinned layer 53.

Further, in another exemplary embodiment, the magnetic tunnel junctionlayer 400 may have a stacked structure of a pinning layer, a pinnedlayer, a tunnel insulating layer, and a free layer, which are formed inorder on the first electrode 23. The pinning layer 63, the pinned layer53, and the free layer 33 may respectively include any material used inabove-mentioned embodiment. The insulating layer 12 may also include anymaterial used in above-mentioned embodiment.

According to exemplary embodiments, the second electrode may covereither a partial area of the pinning layer 63 or whole area of thepinning layer 63.

FIGS. 5A to 5C are plan views depicting a magnetic tunnel junction layerincluded in the MD devices shown in FIGS. 1 to 4.

As shown, in plan views, the magnetic tunnel junction layer has a formof one selected from the group of oval, circle, and rectangular.

FIG. 6 is a perspective view describing a process for fabricating theMTJ devices shown in FIGS. 1 to 4.

As shown, for fabricating an electrode of the MTJ devices, aco-sputtering process is performed because it has an advantage of stepcoverage. In the co-sputtering process, only wafer may be rotated, or awafer and an axis of wafer holder may be rotated and revolvedrespectively. The co-sputtering process may apply to fabrication ofother layers included in the MTJ device.

FIGS. 7A to 7F depict a method for forming the MTJ devices shown inFIGS. 1 to 4.

In the method for fabricating a magnetic tunnel junction device, thereis forming a first electrode. The first electrode has a different shapeaccording to fabrication methods in embodiments of the presentinvention. Then, a magnetic tunnel junction layer is formed on the firstelectrode, and a second electrode is formed on the magnetic tunneljunction layer.

Referring to FIG. 7A, an insulation layer 10 with patterns is formed ona substrate. For gap-fill of the patterns, a first electrode conductinglayer 20 a is formed on the insulating layer 10.

Referring to FIG. 7B, a sacrificial layer 70 is formed on a firstelectrode conducting layer 20 a.

Referring to FIG. 7C, the sacrificial layer 70 is patterned to form asacrificial pattern 70 a. The sacrificial layer 70 may includes aphoto-resist layer, a hard mask layer, or a combination of thephoto-resist layer and the hard mask layer.

Referring to FIG. 7D, using the sacrificial pattern 70 a as an etchmask, the first electrode conducting layer 20 a is etched to form afirst electrode 20 having a bowed top surface.

Referring to FIG. 7E, a junction layer 100 a is formed on the firstelectrode 20.

Referring to FIG. 7F, the junction layer 100 a is patterned to form amagnetic tunnel junction layer 100.

As discussed above, according to exemplary embodiments of the presentinvention, a magnetic tunnel junction (MD) is curved or bowed like adome or convex shape to facilitate securing an area of ferromagneticlayer in scaled-down MD device.

As applying to a STT-RAM or an MRAM, the MD devices according toexemplary embodiments may settle super paramagnetic characteristicappeared in conventional MTJ of scaled-down devices due to limited areaof ferromagnetic layer. In an MRAM including the MTJ device according toembodiments, high density current for controlling a magnetization spindirection of the MTJ device may by no longer applied so that currentconsumption of the MRAM may be reduced.

In accordance with embodiments of the present invention, a spin-transfertorque random access memory or a magnetic random access memory with highintegration and high operation reliability may be fabricated.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1-11. (canceled)
 12. A magnetic tunnel junction device, comprising: afirst electrode having a spherical structure with a protruded pillarpattern; a magnetic tunnel junction layer formed along a sphericalsurface of the first electrode; an insulating layer configured toinsulate the magnetic tunnel junction layer from the protruded pillarpattern of the first electrode; and a second electrode formed on themagnetic tunnel junction.
 13. A magnetic tunnel junction device,comprising: a first electrode having a pillar structure; a magnetictunnel junction layer including a bottom connected to the firstelectrode and a curved top surface; and a second electrode formed on themagnetic tunnel junction.
 14. A magnetic tunnel junction device,comprising: a first electrode having a pillar structure; a magnetictunnel junction layer having a spherical surface and covering an upperpart of the first electrode; a second electrode formed on the magnetictunnel junction; and an insulating layer configured to electronicallyisolate the magnetic tunnel junction from a side area of the upper partof the first electrode.
 15. A method for fabricating a magnetic tunneljunction device, comprising: forming a first electrode having a curvedtop surface; forming a magnetic tunnel junction layer along the topsurface of the first electrode; and forming a second electrode on themagnetic tunnel junction.
 16. The method as recited in claim 15, whereinthe forming of the first electrode includes: forming an insulating layerwith patterns over a substrate; forming a first conducting layer overthe insulating layer to fill the patterns; forming a sacrificial patternover the first conducting layer; and etching the first conducting layerusing the sacrificial pattern as an etch mask to form the top surface ofthe first conducting layer in a convex shape.
 17. The method as recitedin claim 16, wherein the forming of the magnetic tunnel junction layerincludes a co-sputtering process.
 18. The method as recited in claim 16,wherein the sacrificial pattern includes one of a photo-resist layer, ahard mask layer, and a combination thereof.
 19. The method as recited inclaim 15, wherein the magnetic tunnel junction layer is formed to have across section in a shape of one selected from the group of oval, circle,and rectangular.
 20. The method as recited in claim 15, wherein thefirst electrode is faulted in a dome shape.
 21. The method as recited inclaim 15, wherein the first electrode includes a protrusion having acylinder shape at bottom part.